Phosphate coating of metals



Patented Apr. 4, 950

2,502,441 PHOSPHATE COATING F METALS Sidney R. Dodd, West Caldwell, N. Jand Robert F. Ayres, New York, N. Y., assignors to Oakite Products, Inc,New York, N. Y., a corporation 1 .No Drawing. Application November 22,1946,

Serial No. 711,810

1 The present invention relates to improvements ina composition and aprocess for depositing phosphate coating on metal surfaces when employedin phosphate coating solutions, and more particularly to compositionswhich will not only accelerate the deposition of a phosphate coatingupon the surface of metals such as ferrous metals and other metals suchas aluminum, zinc, magnesium and template, but also condition thecoating obtained by improving the quality he o It is therefore an'object'of the invention to provide a composition which, when added to aphosphate coating solution, will cause accelerated deposition ofphosphate coatings on ferrous and other metal objects treated with suchsolution. It is another object to provide a composition which will, whenadded, to phosphate coating solutions, promote uniformity, hardness, andadherence of phosphate coatings obtained when treating metal objectswith such solution.

It is a further object to provide an improved method of producingphosphate coatings on metal Larti'cles employing the novel phosphatecoating solutions. V

A' proposal has already been made in German Patent No. 584,411 to addwater soluble'molybdenum compounds to phosphating baths in order toprovide accelerated deposition of a coating containing a mixture ofphosphates and molybdenumoxides. However, it has been found thatcoatings produced from such baths containinga molybdenum compound tendto have poor adherence to the metal surface and have an undesirable softor spongy nature rendering them inefficient as rust retarders and'ofpoor quality in forming a strong bond with paint, enamel and otherorganic finishes.

"In accordance with the present invention, it has been found thatconsistently uniform, adherent and hard phosphate coatings, which alsohave excellent corrosion resistant and paint bonding properties, may beobtained if the phosphating solution is employed to which a smallquantity of a water soluble molybdenum or tungsten'compound suchfas themolybdic and tungsti'c acid compounds, molybdic acid, tungsticacid,:their anhydrides,v and their. .water soluble salts, and a smallquantity of a phenolic substance, such as, for example, the tannins,tannin n'uclei,. and tannin derivatives have been added. I .The additionof such molybdenum or tungsten compound. in combination with a phenoliccompound not only. accelerates and promotesthe Claims. (Cl. 148-615)production of a phosphate coating, but also pro-, duces desirableeifects in the quality and consistency of the coating obtained.

. It has also been found that phosphate coating solutions, in which themajor ingredient is a primary phosphate of the alkali group, that is,the primary alkali metal or ammonium phosphates, will give goodphosphate coatings when they contain a small quantity of the novelaccelerating combination in accordance with the invention. In theabsence of such accelerating combination little or no phosphate coatingis obtained from solutions containing suchphosphates.

In addition, the use of the accelerating combination in accordance withthe invention renders it possible to reduce the amount of freephosphoric acid usually present in solutions of which the majorconstituent is a monobasic phosphate of a heavy metal, such as zinc,manganese, or iron. In other words, phosphate coating solutions may beemployed in accordance with the inventionat a higher pH than in usualpractice, namely, at a pH of about 3.2 to about 5.5 instead of at about2.5.

"Molybdenum compounds are preferably employed in accordance with theinvention, but tungsten compounds possess similar properties. Thefollowing compounds are, for example, suitable: ammonium, sodium,potassium, molybdates and tungstates, and molybdic and tungstic' acidsand acid anhydrides. The quantity of molybdenum or tungsten compoundsemployed in'a phosphate coating composition in accordance with theinvention may range from 0.1% to 10% of the quantity of solid acidphosphate "saltpresent. Preferably, the quantity of such compounds usedis between 0.5% and 2.0% as higher concentrations tend toward theproduction of softer coatings.

The phenolic ingredients of the novel composition in accordance with theinvention are preferably tannins, phenolic tannin derivatives andrelated phenolics. However, other phenols,-

such as phenol itself, possess the desirable effect in the combinationinaccordance with the in-' of other suitable phenolics are as follows:'

phenol, catechol, resorcinol, hydroq uinone, pyrogallol, pyrogallicacid, gallic acid, phloroglucinol and the like. The polyhydric phenoliccom-- equal to the quantity of molybdenum or" tungsten compound used.However, the pro-..

portion may be varied within the limits of the quantities given above.

The phenolic compounds and molybdenum or tungsten compounds may be addedseparately or together to a phosphate coating solution or may beincorporated in a solid phosphating composition before preparation ofthe aqueous phosphate coating solution.

It is desirable to incorporate wetting or cleaning agents, which areeffective in acid solution, to phosphate coating solutions prepared inaccordance with the invention, but such wetting or cleaning agents maybe omitted if the metal articles to be coated have been thoroughlycleaned before treatment with the solution.

The following wetting and cleaning agents are,

for example, suitable for use in phosphate coating compositions preparedin accordance with the invention:

Sulphonated fatty alcohols. Alkylated' aromatic sulphonates.

Complex sulphonated amides. Polyhydric alcohol anhydride ethersesterified 3 with fatty acids such as sorbitan monolaurate.

Non-ionic wetting agents such as polyethylene oxide derivatives of fattyalcohols or acids, or of other substances containing hydroxyl orcarboxyl groups.

Any of these are suitable for use as the Wetting and cleaning agentswhich are recited in the examples given below, which will serve toillustrate the invention.

Example 1 A phosphate solution is prepared containing approximately 2ounces per gallon of a composition of the following formula:

Per cent NaHzPOi 90.0 M003 1.0 Quebracho 0.5 Wetting and cleaning agent8.51

This solution when used hot and applied for two minutes by pressurespraying to a ferrous metal surface will convert the surface into aprosphate coating averaging about 100 milligrams in weight per squarefoot of surface.

If the M003 and quebracho are omitted from the same type of acidphosphate solution, consistent deposition of a coating is diflicult toaccomplish. Results are erratic; the coating being non-uniform, meagre,or completely non-existent.

If the molybdenum compound without the tannin is used in the same typeof solution, a deposit results which seems amorphous in structure, isnon-adherent to the surface, and of no value as a foundation forpainting.

If the tannin is used Without the molybdenum compound in such solution,deposition .of a coat ing seemsto be completely inhibited. I

Example 2 An aqueous solution is prepared containing about 2 ounces pergallon of .the following composition:

Per cent NH4I-I2PO4 90.0 M003 1.0 Sumac tannin 1.0 Wetting and cleaningagents 8.0

This solution gives results similar to those obtained in Example 1 whenused in the same manner.

Example 3 A phosphatingbath is prepared containing about 2'ounces pergallon of the following composition:

Per cent NaI-IzPO4 90.5 H3PO4 4.5 Ammonium molybdate 1.0 Catechol 1.0Wetting and cleaning agents 3.0

Immersion of a steel article in such bath for 4 minutes at a temperatureof 160 F. produces about milligrams of a 'hard continuous coating persquare foot of surface.

Example 4 A phosphating bath is prepared containing about 2 ounces pergallon .of the following composition:

Per cent ZnH-;(PO4) 2 p 50.5 H3PO4.(75%) 47.5- MOO; 1.0 Quebracho 1.0

A steel panel immersed insuch bath for 4 minutes at 160 F. will receivea hard coating weighing about milligrams per square foot.

Example 5 A .phosphating solution containing 3 ounces per gallon of thefollowing composition is prepared:

Per cent NaHaPOa. 91.9

H3PO4 4.5 Na2WO4.2I-I2O .6

Quebracho 1.0 Wetting and cleaning agents 3.0

This phosphating solution will produce about 85 milligrams of a hard,continuous, iridescent coating per square foot when used in the sammanner as the solution in Example 3.

Example 6 A phosphating solution containing '3 ounces per gallon of thefollowing :composition is prepared:

' 1 Per cent NaH2PO4' 90.5 H3PO4 75 4.5 Ammonium molybdate 1.0Resorcinol 1.0 Wetting and cleaning agents 3.0

This solution will produce results similar to those described in Examplev3.

While the compositions given. in the .above examples in most instancesinclude wetting and cleaning agents, they may be omitted and equalresults will .be obtained if the metal articles are thoroughly .cleaned;bciorextreatment.

Also, while the phosphate coating solutions may be used in accordancewith the invention at a pH between 3.2 and 5.5, it has been foundpreferable to adjust the pi-I value thereof to between 3.2 and 3.8 whenthe coating is obtained by tank immersion and to adjust the pH valuethereof to 4.8 to 5.2 when a spray machine is used to apply the solutionto the articles being coated.

We claim:

1. A phosphating composition comprising an acid salt of phosphoric acidand a water soluble compound selected from the group consisting ofmolybdic acid compounds and tungstic acid compounds and a phenol, saidlatter two ingredients each being present in a quantity ranging from0.1% to of the quantity of acid salt of phosphoric acid.

2. A phosphating composition comprising an acid salt of phosphoric acidand a water soluble compound selected from the group consisting ofmolybdic acid compounds and tungstic acid compounds and a phenol, saidlatter two ingredients each being present in a quantity ranging from0.5% to 2% of the quantity of acid salt of phosphoric acid.

3. A phosphating composition comprising an acid salt of phosphoric acid,a water soluble compound selected from the group consisting of 'molybdicacid compounds and tungstic acid compounds, and a polyhydric phenol,said latter two ingredients each being present in a quantity rang ingfrom 0.1% to 10% of the quantity of acid salt of phosphoric acid.

4. A phosphating composition comprising an acid salt of phosphoric acid,a water soluble compound selected from the group consisting of molybdicacid compounds and tungstic acid compounds, and a tannin containing atleast one free phenolic hydroxy group, said latter two ingredients eachbeing present in a quantity ranging from 0.1% to 10% of the quantity ofacid salt of phosphoric acid.

5. A phosphating composition comprising an acid salt of phosphoric acid,a water soluble compound selected irom the group consisting of molybdicacid compounds and tungstic acid compounds, and quebracho, said lattertwo ingredients each being present in a quantity ranging from 0.1% to10% of the quantity of acid salt of phosphoric acid.

6.1-1 phosphating composition comprising an acid salt of phosphoricacid, a water soluble molybdic acid compound and a phenol, said lattertwo ingredients each being present in a quantity ranging from 0.1% to10% of the quantity of acid salt of phosphoric acid.

7. A phosphating composition comprising an acid salt of phosphoric acid,a water soluble molybdic acid compound and a polyhydric phenol, saidlatter two ingredients each being present in a quantity ranging from0.1% to 10% of the quantity of acid salt of phosphoric acid.

8. A phosphating composition comprising an acid salt of phosphoric acid,a water soluble molybdic acid compound and a gallic acid, said lattertwo ingredients each being present in a quantity ranging from 0.1% to10% of the quantity of acid salt of phosphoric acid.

9. A phosphating composition comprising an acid salt of phosphoric acid,a water soluble molybdic acid compound and a tannin containing at leastone free phenolic group, said latter two ingredients each being presentin a quantity ranging from 0.1% to 10% of the quantity of acid salt ofphosphoric acid.

10. A phosphating composition comprising an acid salt of phosphoricacid, a water soluble molybdic acid compound and quebracho, said lattertwo ingredients each being present in a quantity ranging from 0.1% to10% of the quantity of acid salt of phosphoric acid.

11. A phosphating composition comprising an acid salt of phosphoricacid, a water soluble molybdic acid compound and catechol, said lattertwo ingredients each being present in a quantity ranging from 0.1% to10% of the quantity of acid salt of phosphoric acid.

12, A phosphating composition comprising an acid salt of phosphoricacid, a water soluble compound selected from the group consisting ofmclybdic acid compounds and tungstic acid compounds, and a phenol, saidlatter two ingredients being present in substantially equal quantities,the quantity of each ranging from 0.1% to 10% of the quantity of acidsalt of phosphoric acid.

13. A phosphating composition comprising a primary phosphate of thealkali group and a water soluble compound selected from the groupconsisting of molybdic acid compounds and tungstic acid compounds and aphenol, saidlatter two ingredients each being present in a. quantityranging from 5.1% to 10% of the quantity of a primary phosphate of thealkali-group.

14. A phosphating composition comprising a primary phosphate of thealkali group, a water soluble molybdic acid compound and quebracho, saidlatter two ingredients each being present in a quantity ranging from0.2% to 5% of the primary phosphate of the alkali group.

15. A process of coating metal surfaces which comprises contacting themetal surfaces with an aqueous solution of an acid salt of phosphoricacid containing a water soluble compound selected from the groupconsisting of molybdic acid compounds and tungstic acid compounds and. aphenol, said latter two ingredients each being present in a quantityranging from 0.1% to 10% of the quantity of the acid salt of phosphoricacid.

SIDNEY R. DODD. ROBERT F. AYRES.

REFERENQES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,254,263 Oeschger Jan. 22, 19181,838,189 Tanner et a1 Nov. 15, 1932 1,893,495 Eberhard Jan. 10, 19331,911,537 Tanner May 30, 1933 1,946,647 Taylor et a1 Feb. 13, 19342,336,071 Clifford et a1 Dec. '7, 1943 2,375,468 Clifford et al May 8,1945 2,385,800 Douty et a1 Oct. 2, 1945 FOREIGN PATENTS Number CountryDate 584,411 Germany Sept. 20, 1933

1. A PHOSPHATING COMPOSITION COMPRISING AN ACID SALT OF PHOSPHORIC ACID AND A WATER SOLUBLE COMPOUND SELECTED FROM THE GROUP CONSISTING OF MOLYBDIC ACID COMPOUNDS AND TUNGSTIC ACID COMPOUNDS AND A PHENOL, SAID LATTER TWO INGREDIENTS EACH BEING PRESENT IN A QUANTITY RANGING FROM 0.1% TO 10% OF THE QUANTITY OF ACID SALT OF PHOSPHORIC ACID. 